The Continuous Electron Beam Accelerator Facility (CEBAF) at the Jefferson Lab in Newport News, Virginia, accelerates electrons through SRF cavities that are maintained at Ultra High Vacuum (UHV) or at less than 10−9 torr.
Deformable metal seals are typically used at the interface between the SRF cavities in order to form a vacuum-tight seal. The SRF cavities are typically joined together by installing and torqueing bolts or similar fasteners between flange joints on the ends of the cavities.
Unfortunately, in the act of assembling the cavities, the metal-to-metal contact between the threads of the bolt and the threads of the flange can produce microscopic contamination particles. If the dust particles are introduced into the SRF cavities, they can heat up and release electrons that interfere with the particles that are being accelerated by the accelerator, a problem called field emission.
Accordingly, it is essential for the proper operation of the accelerator to connect the SRF cavities in a manner that does not cause particulate generation. A reduction in particle generation results in a cleaner processing environment and a marked reduction in the number of cavities exhibiting field emission, which field emission can seriously degrade the performance of the particle accelerator.